1. Field of the Invention
The present invention relates to a bar-code reading device for use in reading bar codes printed on, for example, the outer circumferential surface of a test tube. More particularly, the invention relates to a structure that prevents the bar code on a test tube from being concealed by the holder holding the test tube, at the time of reading the bar code from the test tube.
2. Description of the Related Art
In medical institutions such as hospitals, the blood sampled from a subject is contained in test tubes. The personal data of the subject, including the name, sex and age, and the date and time of blood sampling are printed on a bar-code label. The bar-code label is bonded to the outer circumferential surface of the test tube containing the blood sampled.
In the blood-sampling system hitherto employed in hospitals, the subjects' personal data are acquired at the reception counters. The personal data about each subject, thus acquired, is printed in the form of a bar code on a bar-code label. The bar-code label is bonded to the test tube that will contain the blood to be sampled from the subject. The test tube with the bar-code label on it is transported to the blood-sampling room of the hospital. In the blood-sampling room, the data is read from the bar-code label on the test tube. The data thus read is shown on a display. In accordance with the data displayed, the subject is called into the room. The blood is sampled from the subject. A blood-sampling system of this type is disclosed in, for example, Japanese Patent No. 2739928.
FIGS. 6 and 7 show two types of test tubes 11aand 11b, respectively. Both tubes 11aand 11bare used to contain sampled blood. The test tube 11ashown in FIG. 6 and the test tube 11bshown in FIG. 7 differ in length from each other. In other words, the test tube 11ais a short-type one and the test tube 11bis a long-type one. The test tubes 11aand 11bhave an opening at the top. The opening of each tube is closed with a cap 12. Each of the test tubes 11aand 11bhas a bar-code label 14 that is bonded to the outer circumferential surface of the tube. A bar code 13 is printed on the label 14, showing various data items including the date and time of blood sampling and the name of the subject.
The test tubes 11a and 11b are held in two holders 15, respectively. Each holder 15 has a holder main body 16 that is made of synthetic resin. The holder main body 16 is a hollow cylindrical member that has an opening at the upper end. Through the opening the test tube 11a or 11b can be inserted into the holder 15. The holder main body 16 has a pair of flanges 16a and 16b at the lower end. The flanges 16a and 16b are spaced in the axial direction of the holder main body 16 and arranged coaxial with each other. The holder main body 16 has a guide groove 16c. The guide groove 16c is cut in the outer surface, lying between the flanges 16a and 16b. 
A guide rail 17 holds the holders 15 upright. Held in this position, the holders 15 are transported along the guide rail 17. The guide rail 17 is made of synthetic resin or metal such as aluminum alloy.
The guide rail 17 has a pair of side walls 17a and 17b. The side walls 17a and 17b extend parallel, spaced from each other by a gap. They define a transport path 17c, in which the lower parts of the holders 15 are inserted. The side walls 17a and 17b each have a guide rib 18. The guide ribs 18 extend in the lengthwise direction of the transport path 17c and protrude in the guide groove 16c of each holder main body 16. Thus, the guide ribs 18 are in sliding contact with the holder main bodies 16.
A conveyor belt 19 is arranged at the bottom of the guide rail 17. The conveyor belt 19 runs along the guide rail 17. While so running, the belt 19 contacts the bottoms of the holders 15. The holders 15 are thereby transported along the transport path 17c. 
The transport path 17c has a reading position. When the holder 15 holding the test tube 11a or 11b reaches the reading position, a bar-code reader (not shown) reads the bar code 13 from the bar-code label 14 bonded to the test tube 11a or 11b. 
In the conventional blood-sampling system, the holders 15 have the same size, though the test tubes 11a and 11b differ in length. Further, the test tubes 11a and 11b are inserted deep into the holder main bodies 16, having their lower ends in contact with the bottoms of the holder main bodies 16. Hence, the test tubes 11a and 11b would not slip out of the holders 15 while they are being transported.
While the long-type test tube 11b shown in FIG. 7 is held in the holder 15, the bar-code label 14 on this tube is located above the top of the holder 15. The bar code 13 is therefore exposed in its entirety. No problems will arise in reading the bar code by means of the bar-code reader (not shown).
In the case of the short-type test tube 11a, however, a part of the bar-code label 14 lies inside the holder main body 16. The holder main body 16 inevitably conceals this part of the label 14. The bar-code reader cannot read the bar code 13.
To read the entire bar code 13, the test tube 11a may be inserted in the holder main body 16, not so deep as illustrated in FIG. 6. If the test tube 11a is so inserted, however, the holder main body 16 can no longer firmly hold the tube 11a. The test tube 11a may rattle or may slip out of the holder 15 while it is being transported.